V-belt continuously variable transmission for a vehicle engine

ABSTRACT

A control device for controlling a V-belt CVT (Continuously Variable Transmission) which is connectible to a vehicle engine and comprises a primary variator and a secondary variator. The control device has a plurality of sensors which generate electronic measured values, comprising an engine speed sensor which generates a first measured value, and a power sensor which generates a second measured value which is related to the torque of an output drive shaft connected to the secondary variator. The control device further comprises an electronic control unit which is adapted to control the V-belt CVT based on said measured values. A V-belt CVT having a control device as stated above, and a method for controlling such a V-belt CVT are also provided.

FIELD OF THE INVENTION

The present invention relates to a V-belt CVT (Continuously VariableTransmission) for a vehicle engine and a control device for such a CVT.

BACKGROUND ART

In many types of vehicle powered by an engine, the designer has selecteda V-belt CVT. Such a transmission or drive comprises a primary variatorand a secondary variator. The primary variator is connected to anddriven by the crankshaft of the engine. The motion is transmitted by aV-belt to the secondary variator. The secondary variator is in turnconnected to an output drive shaft that drives a wheel, belt, track orthe like depending on the type of vehicle. Examples of vehicles wherethe V-belt CVT is used are light motorcycles and cross-country vehicles,such as three-wheel or four-wheel off-road motorcycles, weasels andsnowmobiles.

The variator pulleys, on which the V-belt runs, each consist of twopulley halves. The relative distance of the pulley halves is variable soas to allow different gear ratios. Such shifting traditionally occursautomatically and continuously. As a rule the automatic function isestablished by the primary variator having a pulley with a fixed pulleyhalf, i.e. which is fixedly connected to the crankshaft of the engine,and a movable pulley half, which is axially displaceable. Thedisplacement of the movable pulley half is controlled by what isreferred to as a centrifugal clutch with weight arms which, as thepulley rotates, strive to displace the movable pulley half so that thedistance between the pulleys decreases. A return spring strives to pullthe movable pulley half in the opposite direction. From an initialposition with a stationary variator up to an engagement speed where theweight arms act on the movable pulley half by a force that exceeds thespring force, the distance between the pulleys is maximal. By replacingthe spring by a spring with another spring constant and changing thedesign of the weight arms, it is possible to provide differentengagement speeds and operating ranges.

The secondary variator also has a fixed pulley half and a movable pulleyhalf. The movable pulley half is movable both axially and tangentially.A biasing spring presses the movable pulley half against the fixedpulley half and tangentially against a stop. A device with wedge-shapedcams is designed so that the movable pulley half must be displacedtangentially, i.e. rotated about the variator shaft to be able to bedisplaced axially from the fixed pulley half. This device makes thevariator sensitive to torque. With no torque, or only a minor torque, onthe output shaft of the variator, it is only necessary for the axial andtangential bias of the biasing spring to be overcome for the movablepulley half to be displaced from the fixed pulley half. With greatertorques, greater friction is generated between the movable pulley halfand the wedge-shaped cams. The increased friction cooperates with thebiasing spring to keep the pulley halves together.

The construction of the primary variator with weight arms, that areactuated by the rotation and control the distance between the pulleyhalves, is self-regulating and besides results in a fixed operatingbehavior. It is in many cases desirable to be able to easily change thecharacter of the drive.

An attempt to achieve this is disclosed in European Patent ApplicationPublication No. 701 073, Piaggio et al. The object presented in EP 701073 is to provide a V-belt CVT for a light motorcycle where the V-beltCVT in addition to the continuous operating mode also provides anoperating mode where the driver can select a desired ear. This isachieved by an operating linkage which is connected to the movablepulley half of the primary variator and which is operated by a motorizedcam element, which in turn is controlled by an electronic control unit.The driver can select manual or automatic shifting. In the former case,the driver himself increases or decreases the transmission ratio by abutton on the handle bars. In both cases, it is the control unit thatcontrols via the operating linkage the displacement of the movablepulley half, either according to a predetermined operating schedule oraccording to the driver's instructions. The initial setting of theprimary variator, however, is still performed by means of a centrifugalclutch. In the automatic position, the control unit then controls thevariator based on measured values of the speed of the engine and theposition of the throttle lever.

The solution shown in EP 701 073 is certainly applicable to lightmotorcycles that are driven on roads. However, problems arise if you tryto apply the solution to vehicles that are driven under more extremeoperating conditions, such as three-wheel and four-wheel off-roadmotorcycles and snowmobiles, i.e. in the typical case cross-countryvehicles. Such more extreme operating conditions comprise, for example,rapidly and sharply shifting friction between the drive wheel/drivebelt/track and the ground. Under such conditions, the prior-art solutionhas difficulties in continuously providing optimal gear ratio.

SUMMARY OF THE INVENTION

The object of the invention is to provide a V-belt CVT which functionswell also for vehicles that are driven under extreme operatingconditions.

The object is achieved by a control device as claimed in claim 1 and aV-belt CVT as claimed in claim 9.

According to a first aspect of the invention, a control device is thusprovided for controlling a V-belt CVT which is connectible to a vehicleengine and comprises a primary variator and a secondary variator. Thecontrol device has a plurality of sensors which generate electronicmeasured values, comprising at least an engine speed sensor whichgenerates a first measured value, and a power sensor which generates asecond measured value which is related to the torque of an output driveshaft connected to the secondary variator. The control device furthercomprises an electronic control unit which is adapted to control theV-belt drive based on said measured values.

According to a second aspect of the invention, a V-belt drive isprovided, which is adapted to be connected to a vehicle engine, saidV-belt drive comprising a primary variator and a secondary variator, anda control device for controlling the V-belt drive. The control devicehas a plurality of sensors which generate electronic measured values,comprising at least an engine speed sensor which generates a firstmeasured value, and a power sensor which generates a second measuredvalue, which is related to the torque of an output drive shaft connectedto the secondary variator. The control device further comprises anelectronic control unit which is adapted to control the V-belt CVT basedon said measured values.

According to a third aspect of the invention, a control device isprovided for controlling a V-belt CVT which is connectible to a vehicleengine and comprises a primary variator and a secondary variator. Thecontrol device comprises at least one sensor generating an electronicmeasured value. The one or more sensors are selected from a group ofsensors comprising a primary speed sensor, sensing the engine speed or aspeed proportional thereto, a secondary speed sensor, sensing the speedof the secondary variator or a speed proportional thereto, a powersensor generating a measured value related to the torque of an outputdrive shaft connected to the seconddary variator, and a throttle sensor.The control device further comprises an electronic control unit which isadapted to control the V-belt CVT based on said electronic measuredvalue(s), and a clamping power actuator which is connected to thecontrol unit and to the primary variator. The electronic control unit isadapted to set the V-belt clamping power of the primary variator bymeans of the clamping power actuator. According to a fourth aspect ofthe invention, a V-belt CVT is provided, which is adapted to beconnected to a vehicle engine. The V-belt CVT comprises a primaryvariator and a secondary variator, and a control device according tosaid third aspect of the invention.

Thus, according to the invention, it has been realized that either bycombining measured values of at least the speed of the vehicle engineand a magnitude which is related to the torque of the output shaft or byeliminating the centrifugal clutch of the primary variator and, instead,provide an electronically controlled actuator operating on the variator,it is possible to provide a considerably more controllable transmissionwhich besides has considerably better relation to the operatingconditions. For example, the friction against the ground, i.e. the grip,may suddenly practically disappear and then immediately become veryhigh. Under such conditions the V-belt CVT can be set more accurately bya control device according to the invention than by using prior-arttechnique.

According to an embodiment of the control device according to theinvention, the second measured value represents a V-belt clamping powerof the primary variator. The pulley clamping power is a magnitude thatis relatively easy to measure. It is also related to the torque of theoutput drive shaft by the clamping power of the primary variator actingon the pulley, which in turn cooperates with the secondary variator,which in turn is connected to the output drive shaft and on which thetorque thereof is exerted. As described above, the movement of themovable pulley half of the secondary variator is determined by theoutput torque.

In one embodiment of the control device according to the invention, thesecond measured value represents the torque of the output drive shaft.The advantage of this measured value is that it gives direct informationabout the operating conditions prevailing on the output side of the CVTand enables a quickly acting control device.

In one embodiment of the control device according to the invention, thecontrol unit is adapted to control the CVT so that a predeterminedrelationship between the measured values is achieved in each operatingsituation. This gives the advantage of a simple calculation which thecontrol unit is to perform. It also facilitates the work for a personskilled in the art who is to design the character of the drive.Different templates or schedules for the operation, which give differentcharacters, can easily be created by combining the measured values indifferent ways. This is used in one embodiment of the control device toallow it to be set in different operating modes which give differentrelationships between the measured values in a specific operatingsituation. This embodiment can advantageously be used as follows. Adriver of a vehicle with an engine whose V-belt CVT is controlled by acontrol device according to the invention can be given an opportunity toset different operating modes by himself. Depending on the groundconditions, the driver's personality etc, an individual andsituation-adapted setting of the character of the V-belt CVT can thus beprovided. In contrast to the construction shown in EP 701 073, thechange in the gear ratio of the CVT in response to a change of theoperating conditions, such as friction against the ground, can thus beset. For instance, an increase or decrease of the gear ratio, i.e.shifting, may occur according to a steeper or flatter curve. Moreover,for instance said increase/decrease can occur at different degrees ofsteepness in different parts of a total operating range. This will bedescribed and exemplified in more detail below.

In one embodiment, the control device according to the inventioncomprises a clamping power actuator which is connected to the controlunit and adapted to set the pulley clamping power of the primaryvariator, in which case the control unit controls the actuator. By suchcontrolled setting of the clamping power, the second measured value canbe used in an advantageous manner.

In one embodiment of the control device, the control unit is adapted tocommand the clamping power actuator to cause engagement of the primaryvariator at a settable first engine speed and to set the actuator tomaximum clamping power at a settable second engine speed. At leastaccording to this embodiment, it is possible to simplify a primaryvariator of the above-described frequently used prior-art construction,implying that the centrifugal clutch can be excluded. Instead it will bethe control unit that fully determines the position of the movablepulley half in relation to the fixed pulley half. The actuator activelyperforms the setting at all speeds in contrast to the engagementperformed by the centrifugal clutch, which is disclosed in EP 701 073and which is not settable for different speeds unless a mechanicalmodification of the primary variator is made. Thus, this embodimentresults in more freedom in the designing of the character of the V-beltCVT. Both the first speed, i.e. the engagement speed, and the secondspeed, i.e. the maximum speed, are settable.

In one embodiment of the V-belt CVT, the primary variator comprises,like the above-described prior-art primary variators, a fixed pulleyhalf which is fixedly connectible to the crankshaft of the engine, and amovable pulley shaft which is displaceably connectible to thecrankshaft. Moreover the actuator comprises a holding-up means, which isarranged at a fixed distance from the fixed pulley half, a firstoperating arm which is connected to the movable pulley half, a secondoperating arm which is connected to the holding-up means, and a settingarm, which is adapted to set the distance between the operating arms.This embodiment has a robust construction of the actuator.

In one embodiment of the V-belt CVT, the setting arm is elongate andcomprises spaced-apart first and second guide portions, which abutagainst abutment portions of the first and the second operating arm,respectively. The distance between the guide portions increases awayfrom one end of the setting arm towards its other end, and the settingarm is displaceable back and forth in its longitudinal direction. Thusforcing the operating arms apart by means of the non-parallel guideportions of the setting arm can be resembled to driving a wedge betweentwo parts and results in direct and powerful transmission of the settingpower. Moreover this embodiment adds an additional control option bymaking it possible to select different degrees of steepness in theincrease of the distance between the guide portions. For instance, byselecting a constant speed of the displacement of the setting arm in thelongitudinal direction while providing a straight and a curved guideportion, the distance between the operating arms will be changed atdifferent speeds depending on where along the guide portions theabutment against the abutment portions is positioned.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and additional advantages thereof will now be described inmore detail by way of example and with reference to the accompanyingdrawings, in which

FIG. 1 is a highly schematic top plan view of a snowmobile with a V-beltCVT according to the invention;

FIG. 2 is a schematic view seen obliquely from above of an embodiment ofan actuator according to the invention;

FIG. 3 is a schematic side view of the actuator in FIG. 2;

FIG. 4 is a block diagram of an embodiment of the control deviceaccording to the invention;

FIGS. 5 and 6 schematically illustrate in a side view and a top planview, respectively, an alternative embodiment of the actuator.

DESCRIPTION OF EMBODIMENTS

For illustrating and exemplifying purposes, the invention will bedescribed in more detail in a realization in the form of a snowmobile,as shown highly schematically in FIG. 1, where some schematic contoursof parts of a snowmobile are drawn. The snowmobile 1 is provided with afour-stroke internal combustion engine 3. The engine 3 is connected to aV-belt CVT 5 which comprises a primary variator 7, a secondary variator9 and a V-belt 11. The primary variator 7 is connected to a drivingshaft of the engine 3, more specifically the crankshaft 13 of theengine. The secondary variator is connected to a driven shaft 15 whichin turn is connected to an output drive shaft 17. The output drive shaft17 makes a track 19 run over support rollers. The track 19 is in contactwith the ground, which preferably consists of snow, and while rotatingpropels the snowmobile. A clamping power actuator 21, which most of thetime is below merely referred to as an actuator, according to acurrently preferred embodiment, is connected to the primary variator 7for setting the same.

The construction of the clamping power actuator 21 will be elucidated inFIGS. 2 and 3, where the actuator 21, the primary variator 7 and aconnection between them are illustrated. The primary variator 7comprises a pulley with a fixed pulley half 23, which is fixedlyconnected to the crankshaft 13, and a movable pulley half 25, which isaxially displaceably connected to the crankshaft 13. The movable pulleyhalf 25 thus is displaceable along the crankshaft 13 but is entrained inthe rotation of the crankshaft 13 by drivers mounted on the crankshaft13, which however are concealed in the Figures by the movable pulleyhalf 25. The actuator 21 comprises a holding-up means 27 which isarranged at a fixed distance from the fixed pulley half 23 at the end ofthe crankshaft 13. The holding-up means 27 comprises a bearing 29mounted on the crankshaft 13 and a bearing holder 31 connected to thebearing 29. The actuator 21 further comprises a first operating arm 33,a second operating arm 35, a piston cylinder assembly 37, a setting arm39 and a shifting motor 41.

The first operating arm 33 is pivotally connected to the movable pulleyhalf 25 by the operating arm 33 at one end 43 being pivotally connectedto a bearing 45, which in turn is connected to the movable pulley half25.

The second operating arm 35 is at one end 47 pivotally connected to thebearing holder 31 of the holding-up means 27. The second operating arm33 is at its other end 49 pivotally connected to the first operating armvia a link 51.

The piston cylinder assembly 37 is connected to the shifting motor 41,which drives the reciprocating piston motion of the piston cylinderassembly 37. The piston rod 55 of the piston cylinder assembly 37 is atits free end connected to the setting arm 39. The cylinder 53 of thepiston cylinder assembly 37 is at one end pivotally connected to theother end 57 of the first operating arm 33.

The setting arm 39 is elongate and comprises first and second guideportions 59 and 61 respectively, which abut against abutment portions58, 60 of the operating arms 33, 35. More specifically, the first guideportion 59 abuts against a first abutment portion 48 which constitutes aportion of the bottom of a groove in a first wheel 63 which is rotatablymounted on the first operating arm 33. The second guide portion 61 abutsagainst a second abutment portion 60 which constitutes a portion of thebottom 67 (see also FIG. 3) of a groove in a second wheel 65, which isrotatably mounted on the second operating arm 35. The first and secondguide portions 59, 61 constitute portions of a first straight edgesurface 62 and, respectively, a second opposite edge surface 64 of thesetting arm 39. The second edge surface 64 is not parallel to the firstbut is either curved or angled in the longitudinal direction of thesetting arm, so that the width of the setting arm 39, over a distance ofthe setting arm 39, increases from its front end 38 towards its rear end40.

By the reciprocating motion of the piston 55, the setting arm 39 isdisplaceable back and forth between the wheels 63, 65. This makes thedistance between the wheels 63, 65 adjustable.

The clamping power actuator 21 constitutes a part of a control devicewhich is shown in the form of a block diagram in FIG. 4. The controldevice further comprises an electronic control unit 73, a plurality ofsensors, which consist of an engine speed sensor 75, a power sensor 77,a locking switch 81 and an operating mode selector 82. The control unit73 is connected to all the other parts included in the control device.As an extra alternative, it is in any case possible to arrange athrottle sensor 79, which will be explained in more detail below.

The control device 71 operates as follows. The control unit 73 collectselectronic measured values in the form of, for example, voltage signals,PWM signals, pulse trains, etc, from the sensors 75, 77 (and 79),processes them, generates a control value and supplies it to theactuator 21. The actuator 21 comprises a motor drive unit 83 whichreceives the control value and, based on the control value, drives theshifting motor 41 forwards or backwards or makes it stand still. Theshifting motor 41 in turn drives the piston cylinder assembly 37, sothat the piston 39 moves either forwards/outwards or backwards/inwardsor does not move at all. As the piston 55 moves forwards and drives thesetting arm 39, the width of the setting arm portion positioned betweenthe wheels 63, 65 increases, i.e. the distance between the guideportions 59, 61 which abut against the wheels 63, 65 increases.

More specifically, the engine speed sensor 75 generates a measuredvalue, which varies with the speed of the internal combustion engine 3.In this embodiment, the control unit 73 converts the signal from theengine speed sensor 75 to a measured value in the form of a percentagebetween 0 and 100%, which corresponds to an operating range of theengine 3. If, for instance, the operating range is determined to be2,000-6,000 rpm, 0% corresponds to 2,000 rpm and 100% corresponds to6,000 rpm. The power sensor 77 consists in this embodiment of fourstrain gages 77, which are linked in a full-bridge architecture andarranged two on each side of the first operating arm 33. The powersensor 77 will then be actuated when the operating arms 33, 35 areforced apart by the setting arm 39. The force exerted by the setting arm39 on the wheels 63, 65 to force the operating arms 33, 35 apartproduces via the movable pulley half 25 a clamping power on the pulley11. The clamping power is in turn related to a corresponding clampingpower in the secondary variator 9. Since the clamping power in thesecondary variator is in turn related to the torque of the output driveshaft, the measured value generated by the power sensor 77 is alsorelated to said torque. The control unit 73 converts also this sensorsignal to a percentage measured value, where 0% corresponds to theminimum clamping power, i.e. 0 N, while 100% corresponds to the maximumclamping power, for instance 3,000 N.

The control unit 73 strives to control the transmission so that arelationship between the measured values from the sensors 75, 77 isachieved. The relationship is given by predetermined operatingconditions which are indicated in an operating template. There aredifferent operating modes which the driver can select by means of theoperating mode selector 82. The different operating modes correspond todifferent operating templates and produce different characters in theshifting of the transmission. The control unit 73 starts from the enginespeed and compares the measured value thereof with the measured value ofthe clamping power. If the clamping power at the current speed is belowwhat has been determined in the currently selected operating template,the control unit 73 produces a control signal to the motor drive unit 83to drive the shifting motor 41 in a direction that increases theclamping power, i.e. that forces the operating arms 33, 35 furtherapart. Consequently, each engine speed corresponds to a predeterminedclamping power between the pulley halves 23, 25 of the primary variator7. In a basic operating mode, a certain percentage of the speedcorresponds to the same percentage of the clamping power. There are alsooperating modes with non-linear relations between the speed and theclamping power. The driver of the snowmobile can himself at any timechange the operating mode among the predetermined operating modes bymeans of the operating mode switch 82.

The control signal also contains information about how quickly thechange is to occur. If the difference between the current measured valueof the clamping power and the desired value according to the operatingtemplate is great, the setting arm 39 is driven more quickly than in thecase of a small difference. New measured values are read continuously bythe control unit 73. In this embodiment it is also possible to vary thesetting character of the actuator 21. This is done by programming in thecontrol unit 73 and, more specifically, in a control program executed bythe control unit 73. As an alternative, the control unit 73 may use, inaddition to the speed and the clamping power, a measured value from thethrottle sensor 79. In this embodiment the throttle sensor 79 generatesa measured value in the form of a voltage signal, where the lowestvoltage corresponds to idling and the highest voltage corresponds tofull throttle. The additional information about the position of thethrottle lever can then be used to make controlling more sensitive andquicker. If the position of the throttle lever is known, it is known inwhich direction the driver wishes to drive the engine speed, and it isthen possible to operate the actuator faster, i.e. the clamping powercan be increased/decreased more rapidly. On the other hand, this mayresult in an operating behavior that is experienced as nervous if theoperation of the actuator is too fast. However, it is possible to chooseto merely activate the increased operation rate in an extreme positionof the throttle lever which is close to maximum. It is then desirable toperform a quick downshift, and a kind of kick-down function is executed.For instance the control unit 73 can determine the magnitude of thechange of the position of the throttle lever per unit of time and usethe result to determine the magnitude of the downshift. The control unit73 then controls the actuator 21 accordingly.

The locking switch 81 is used to lock the control unit 73 so that thecurrent gear ratio is maintained even if the engine speed changes. Thisfunction can be used, among other things, to increase the engine brakeand to produce an engagement speed which is increased in relation towhat is determined by the current operating mode.

The latter may result in a quicker start in a race when the speed of theengine 3 of the snowmobile can be allowed to increase to a speed desiredby the driver before engagement occurs and the drive of the track 19thus begins.

Alternative Embodiments

The above description merely constitutes a non-limiting example of howthe device according to the invention can be designed. Manymodifications are conceivable within the scope of the invention asdefined in the appended claims. A few examples of such modificationswill follow below.

The control of the CVT is based on one or more sensor values. In a mostsimple form only a primary speed sensor, such as the engine speed sensor75, is provided. On condition that the actuator acts on the primaryvariator for fully controlling the distance between the pulley halves,i.e. including engagement and disengagement of the belt, this isacceptable for some kinds of vehicles, where a precise control of thegear ratio is not a critical issue.

According to an alternative embodiment of the control device, theprimary speed sensor 75 is combined with a secondary speed sensor 84, asindicated with dashed lines in FIG. 4. Thereby the gear ratio of thetransmission is controlled. This is enough in yet further applications,while the combination of primary speed sensor 75 and power sensor, asdescribed above, provides a load adaptive control, which is more usefuland precise in some applications.

In embodiments where a plurality of sensors are used, alternatively, thecontrol unit is programmed to detect sensor failures and disregard fromthe values received from a defective sensor. Then the control unit basisits control on the measured values from the remaining correctly workingsensor or sensors.

FIGS. 5 and 6 illustrate an alternative embodiment of the actuator. Theparts that are equivalent to those in the embodiment shown in FIGS. 2and 3 have been given the same reference numerals. The setting arm 91here comprises a center shaft 93 which at one end is pivotally connectedto the second operating arm 35, and at its other end is fixedlyconnected to the housing of the shifting motor 41. The setting arm 91further comprises a sleeve 95 which is rotatably mounted on the centershaft 93 and externally mounted in a holder 97 arranged on the firstoperating arm 33. The sleeve 95 is rotatable but not axiallydisplaceable in the holder 97. Moreover, at least a portion of thesleeve 95 is provided with an inner thread, while the center shaft 93 isprovided with a corresponding outer thread that engages the inner threadof the sleeve 95. The sleeve 95 is also connected to the shifting motor41. The shifting motor 41 rotates the sleeve 45, the threadedconstruction moving it along the center shaft 93 and thus entraining thefirst operating arm 33 so that the distance between the movable pulleyhalf 25 and the fixed pulley half 23 is changed.

An alternative to arranging the power sensor on an operating arm is toprovide the output drive shaft with a power sensor that measures thetorque directly on the shaft. This is achieved, for example, by theshaft being designed so that the current torque causes a suitablerotation of the shaft. The rotation is measured by measuring adislocation of position sensors at both ends of the shaft. The V-beltCVT according to the invention is usable not only in snowmobiles, butalso in many other types of vehicle. A common feature is that theoperating conditions are extreme insofar as the drive wheel or drivewheels, the track, the drive belt etc. encounters significantly morevarying grounds than a common road vehicle. One example is a four-wheeloff-road motorcycle where at one time little energy is required to driveit on hard and dry ground on a slight uphill slope, and at the nextmoment the drive wheels are running in mud and the inclination isgreater. The combination of the measured values of engine speed andclamping power, which ultimately constitute a measure of the energytransmitted to the drive wheels, then allows rapid and smooth automaticadjustment to the new operating conditions.

It should be noted that the sensors described above can be electronic orelectromechanical, wherein, for example, a mechanical, pneumatic orhydraulic part is used for catching a parameter and a converting partperforms a conversion into an electronic output, that is then receivedand processed by the control unit. As a consequence, a sensor can be acompact unit as well as a distributed structure where a converting partis located at a distance from the rest of the sensor, for example closeto the control unit.

It should be emphasized that the embodiments described above are onlynon-limiting examples. Many other variants are conceivable within thescope of the invention as defined in the claims. As additional examplesof alternatives, mention can be made of other engine types, othervariator constructions, etc.

1. A control device for controlling a V-belt CVT which is connectible toa vehicle engine and comprises a primary variator and a secondaryvariator, the control device having a plurality of sensors whichgenerate electronic measured values, comprising an engine speed sensorwhich generates a first measured value, and a power sensor whichgenerates a second measured value, which is related to the torque of anoutput drive shaft connected to the secondary variator, and anelectronic control unit which is adapted to control the V-belt CVT basedon said measured values.
 2. A control device as claimed in claim 1,wherein the second measured value represents a V-belt clamping power ofthe primary variator.
 3. A control device as claimed in claim 1, whereinthe second measured value represents the torque which is exerted on theoutput drive shaft.
 4. A control device as claimed in claim 1, whereinthe control unit is adapted to control the CVT so that a predeterminedrelationship between the measured values is achieved in each operatingsituation.
 5. A control device as claimed in claim 4, wherein thecontrol device is settable in different operating modes which givedifferent relationships between the measured values in a specificoperating situation.
 6. A control device as claimed in claim 1, furthercomprising a clamping power actuator which is connected to the controlunit and to the primary variator, that the clamping power actuator isadapted to set the V-belt clamping power of the primary variator, andthat the control unit's control of the V-belt CVT comprises control ofthe clamping power actuator.
 7. A control device as claimed in claim 6,wherein the control unit is adapted to command the clamping poweractuator to switch on the primary variator at a settable first enginespeed and to set the actuator to maximum clamping power at a settablesecond engine speed.
 8. A control device as claimed in claim 6, furthercomprising a locking switch which is switchable to a locking positionwhere it locks the actuator in its current position.
 9. A V-belt CVTwhich is adapted to be connected to a vehicle engine, said V-belt CVTcomprising a primary variator and a secondary variator, and a controldevice for controlling the V-belt CVT, the control device having aplurality of sensors which generate electronic measured values,comprising an engine speed sensor which generates a first measuredvalue, and, a power sensor which generates a second measured value,which is related to the torque of an output drive shaft connected to thesecondary variator, and an electronic control unit which is adapted tocontrol the V-belt CVT based on said measured values.
 10. A V-belt CVTas claimed in claim 9, further comprising a clamping power actuatorwhich is connected to the control unit and to the primary variator, inthat the clamping power actuator is adapted to set the V-belt clampingpower of the primary variator, and in that the control unit's control ofthe V-belt CVT comprises control of the clamping power actuator.
 11. AV-belt CVT as claimed in claim 10, the primary variator comprising apulley with a fixed pulley half which is fixedly connectible to thecrankshaft of the vehicle engine, and a movable pulley half which isdisplaceably connectible to the crankshaft, wherein the actuatorcomprises a holding-up means which is arranged at a fixed distance fromthe fixed pulley half, a first operating arm which is connected to themovable pulley half, a second operating arm which is connected to theholding-up means, and a setting arm which is adapted to set the distancebetween the operating arms.
 12. A V-belt CVT as claimed in claim 11,wherein the setting arm is elongate and comprises spaced-apart first andsecond guide portions which abut against abutment portions of the firstand the second operating arms respectively, that the distance betweenthe guide portions increases away from one end of the setting armtowards its other end, and that the setting arm is movable back andforth in its longitudinal direction.
 13. A V-belt CVT as claimed inclaim 9, wherein the second measured value represents a pulley clampingpower of the primary variator.
 14. A cross-country vehicle comprising aV-belt CVT as claimed in claim
 9. 15. A cross-country vehicle as claimedin claim 14, wherein the cross-country vehicle is a snowmobile.
 16. Amethod for controlling a V-belt CVT which is connected to a vehicleengine and comprises a primary variator and a secondary variator,comprising the step of detecting and generating a first electronicmeasured value which is related to the speed of the vehicle engine,comprising the steps of detecting and generating a second electronicmeasured value which is related to the torque of an output drive shaftconnected to the secondary variator; and controlling the V-belt CVTbased on said first and second measured values.
 17. A control device forcontrolling a V-belt CVT which is connectible to a vehicle engine andcomprises a primary variator and a secondary variator, the controldevice having at least one sensor generating an electronic measuredvalue, said at least one sensor being selected from a group of sensorscomprising a primary speed sensor, sensing the engine speed or a speedproportional thereto, a secondary speed sensor, sensing the speed of thesecondary variator or a speed proportional thereto, a power sensorgenerating a measured value related to the torque of an output driveshaft connected to the secondary variator, and a throttle sensor,wherein the control device further comprises an electronic control unitwhich is adapted to control the V-belt CVT based on said electronicmeasured value, and a clamping power actuator which is connected to thecontrol unit and to the primary variator, wherein the electronic controlunit is adapted to set the V-belt clamping power of the primary variatorby means of the clamping power actuator.
 18. A control device as claimedin claim 17, wherein said at least one sensor consists of the primaryspeed sensor.
 19. A control device as claimed in claim 17, wherein saidat least one sensor consist of the primary speed sensor and thesecondary speed sensor.
 20. A control device as claimed in claim 17,wherein said at least one sensor consist of the primary speed sensor andthe power sensor.
 21. A control device as claimed in claim 17, whereinthe control unit is adapted to command the clamping power actuator toswitch on the primary variator at a settable first engine speed and toset the actuator to maximum clamping power at a settable second enginespeed.
 22. A V-belt CVT which is adapted to be connected to a vehicleengine, said V-belt CVT comprising a primary variator and a secondaryvariator, and a control device according to claim
 17. 23. A V-belt CVTas claimed in claim 22, the primary variator comprising a pulley with afixed pulley half which is fixedly connectible to the crankshaft of thevehicle engine, and a movable pulley half which is displaceablyconnectible to the crankshaft, wherein the actuator comprises aholding-up means which is arranged at a fixed distance from the fixedpulley half, a first operating arm which is connected to the movablepulley half, a second operating arm which is connected to the holding-upmeans, and a setting arm which is adapted to set the distance betweenthe operating arms.
 24. A control device as claimed in claim 7, furthercomprising a locking switch which is switchable to a locking positionwhere it locks the actuator in its current position.